AT-HOME VERSUS RESEARCH DOSING
Why the discrepancy?
TAKEAWAYS/HIGHLIGHTS
-Subjective markers of optimal dosing probably hold some relevance.
-Based on subjective markers, somewhat exceeding the doses seen in much of the research appears to be appropriate.
-Reflection off the skin when using devices at a distance reduces the amount of light absorbed, increasing the amount needed.
-Using LEDs instead of lasers, which have a wider beam angle, may increase the amount of light needed.
Glossary:
Photobiomodulation(PBM)/LLLT/LEDT: Some of the terms often used in research for red light therapy. LLLT stands for low level laser therapy, or low level light therapy. LEDT stands for Light-Emitting Diode Therapy.
Strength training
TOTAL DOSES IN RESEARCH
The total doses used in red light therapy research are often surprisingly low, especially when considering the amount of light one is exposed to on a typical sunny day outdoors. The doses we typically recommend are higher than one would expect based on the research. There are a number of reasons for this that we'll get into in this article. A good quote from a 2013 review [1] is: “This finding makes sense because the light emanating from LEDs has a wider bandwidth, is not coherent, and is more divergent than the light emanating from laser diodes, resulting in more reflection and less transmission of LED-generated light through the skin. Therefore, a higher dose when using LED therapy may compensate for beam reflection and divergence.” This only covers some of the potential discrepancy, however, and we'll get into more reasons as the article progresses.
Michael Hamblin
To help us answer some of the questions regarding large LED panels, at-home dosing, and how it compares to research dosing, often with small surface areas, we got in touch with prominent red light therapy researcher Michael Hamblin:
CytoLED: Do you think subjective metrics are good for judging when an ideal dose is reached? Perhaps a certain feeling of “satiety” with the light.
Michael Hamblin: I think that this is an interesting idea. Different individuals have differing degrees of susceptibility to light, and what is too much for one person may be nowhere (near) enough for another person. If you have noticed a feeling of “satiety” then this may indicate that that individual needs relatively lower doses. It will however be difficult to be objective.
CytoLED: Do you think there are benefits to much higher doses in terms of total joules than most of the research uses, if they are spread out fairly uniformly across a larger surface area?
Michael Hamblin: I think that the most important measure of dose is total Joules spread over a large area (hundreds or thousands of sq cm). Several tens of thousands of J, if not >100,000 J spread over say 2000 cm2 is only 50 J/cm2. Remember that one hour sunbathing (with sunscreen) at midday equals 1 million total J of optical energy.
CytoLED: Do you have some general thoughts on whole-body or half-body photobiomodulation with fairly high doses, using an LED setup from a distance? Do you have any recommendations for general wellness starting guidelines for full body treatments in terms of power, intensity, time, dose, and total joules?
Michael Hamblin: Large LED panels are an easy way to deliver PBM to the body. More light will penetrate if the panel is in contact with the skin but at a distance is also OK. I often say that light is cheap so you can afford to throw a lot of it away. In general [for full-body use] total optical power should be a few hundred Watts. 200W spread over 10,000 cm2 is 20 mW/cm2. That will be 120,000 J in 10 min or 240,000 J in 20 min.
These answers should emphasize a key point, which is that full-body treatment requires quite a high total power output to even reach typical research dosage parameters for a given area.
Vladimir Heiskanen
Another person we asked for input was Vladimir Heiskanen, someone well-known in the community of red light therapy research enthusiasts for compiling an extensive research database on the topic and publishing academic papers in this area:
CytoLED: What would you say the typical power density used in research is roughly? Perhaps you can give us an approximate range that the majority of studies fall within.
Vladimir Heiskanen: Most studies utilizing light-emitting diodes (LEDs) usually use power densities between 10 and 50 mW/cm2. I would estimate that average duration of a session is 10 minutes. Sometimes it is 2 minutes, sometimes it is 20 minutes.
CytoLED: Dr. Michael Hamblin seems to think total joules is an important marker when it comes to dosing red light therapy. Do you think the power density has a relationship with the surface area, such that larger surfaces need a lower power density, perhaps because the surrounding tissue is also being irradiated and may have an impact?
Vladimir Heiskanen: Some animal studies have shown systemic effects from photobiomodulation. For example, there has been research showing neuroprotective effects from body irradiation. There is still insufficient data for researchers to infer how these effects occur, but I think that it's tempting to hypothesize that the skin, nowadays considered as an endocrine organ, might mediate some of these effects.
CytoLED: Do you think there is sometimes a situation where the more superficial tissue should be overdosed a bit, to get an optimal dose to the deeper tissue?
Vladimir Heiskanen: In animal studies, the research is usually done with small-sized animals such as mice. If one wants to irradiate a brain of a mice, it's relatively easy because the skull is extremely thin and most of the light penetrates through it. However, when you think about large animals such as humans, the skin and underlying tissues can absorb a very high percentage of light. This might even explain why some early photobiomodulation studies for acute stroke in humans failed. They used relatively low doses, which probably did not even reach the brain. Therefore I think that in humans, there is a rationale for considering much higher doses to reach deeper tissues.
CytoLED: Do you think a subjective sense of satiety can be a good indicator to use when dosing full-body red light therapy?
Vladimir Heiskanen: So far, there are no known means to monitor the photobiomodulation response during a treatment session. Subjective feelings could be used as a guideline, but it is not known in which manner the subjective feelings reflect a true physiological response.
CytoLED: Do you think that in the future we'll see a trend towards more research into full-body irradiation with red and near-infrared light (probably using LED panels)?
Vladimir Heiskanen: It is likely that there will be an increasing amount of red light therapy research with LED lights during the next years. So far, there have been very few full-body irradiation studies. I assume there will be more during the next 3-5 years, because there are many large-sized LEDs currently on the markets, and they are becoming increasingly popular.
CytoLED: Do you have any general thoughts on full-body red light therapy, key takeaways from the literature, and dosage suggestions?
Vladimir Heiskanen: There is very limited research on this. A single study with Chinese basketball players [2] used a total energy density of 30 J/cm2 for whole-body irradiation, and they reported some improvement in sleep quality. That dose can be applied with a 10-minute session of 50 mW/cm2 or a 20-minute session of 25 mW/cm2.
Based on what Vladimir has said, we might infer that the optimal dose for full-body (or half-body) red light therapy may depend on the desired tissue depth, and that the subjective sense of “satiety” may or may not relate to optimal dosing at the level of the skin, or perhaps there's a middle ground between tissues at various depths. Given the absence of other metrics to use, we feel it's good to aim for a dose that's somewhere in the general area of the doses the majority of research uses, probably on the higher end for reasons we'll outline below, and use the subjective sense of “satiety” to determine the exact dose/time spent in the light.
Skin Reflection And Air
Let's look at some potential reasons for the discrepancy between research and at-home doses, starting with reflection and air. Most studies using LED panels have them pressed up against the skin. When a light is pressed up against the skin, the light will reflect off the skin, back onto the device, and back onto the skin, and so forth. This is not how we recommend using our panels, the reason for this is that we think it's better to be positioned at a distance where the individual beams converge, and the light is more evenly spread across the surface. For most of our lights, the 30 degree beam angle models, adequate convergence of the beams happens around 50cm, so we recommend this as a minimum distance. When using the light at a distance, more light gets lost due to reflection off the skin (note that this isn't a problem with CytoLED lights due to them being powerful enough to compensate for that). Another thing that will happen at a distance is that the light travels through air, hitting particles, which makes it lose a little potency as well. Both of these factors make it such that a higher amount of energy is required when using a device from a distance at home, compared to the typical research setup of having the light pressed up against the skin.
Beam Angle
Next up is the beam angle. Lasers generally have a very narrow beam angle, very close to 0, and this is desired, for many applications. In practice, it means lasers maintain the irradiance (mW/cm2) at long distances very well, especially if it weren't for air/particles being in the way, a well-made laser in space can go a long way. With lasers, the irradiance is pretty much “what you see is what you get”, in the sense that the irradiance at the point of origination and the point that it's hitting, as long as they're reasonably close, isn't hugely different. With LEDs this can be another story, the natural beam angle of an LED is 180 degrees. However, with reflectors and lenses, as we use in our lights, this beam can be narrowed down and focused. Because we want to irradiate a large area, and have a limited number of LEDs, we need to make sure the individual beams converge at a reasonable distance, while also making sure that the beam angle is narrow enough to maintain irradiance at a distance. Besides the irradiance-drops at a distance in LEDs vs lasers, there is another factor to consider, the angle at which the light hits the skin. A laser can hit the skin in a straight, perpendicular way, a divergent LED beam won't. However, this may have relatively little relevance in practice, especially when irradiating large areas of the body, as they aren't flat anyway. Also, some have argued that the light scatters as soon as it hits the skin anyway.
Conclusions
When taken together, all these pieces of information suggest:
-When irradiating particular areas, it's a good idea to stay on the higher end of the research-doses, using our lights for 10-20 minutes achieves this, but watching for the response and experimenting oneself with what's ideal is also recommended, as there is variance between individuals.
-When irradiating the entire body, or half of the body, we want a large amount of total light energy, and the subjective sense of “satiety” is likely to be the best available guideline when doing this at home.
What have been your experiences dosing at-home red light therapy? Feel free to shoot us an email at info@cytoled.com or hit us up on any of our social media.
References
1. Borsa et al. “Does phototherapy enhance skeletal muscle contractile function and postexercise recovery? A systematic review”. J Athl Train. 2013 Jan-Feb; 48(1): 57–67. doi: 10.4085/1062-6050-48.1.12 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3554033/
2. Zhao et al. “Red Light and the Sleep Quality and Endurance Performance of Chinese Female Basketball Players” J Athl Train. 2012 Nov-Dec; 47(6): 673–678. doi: 10.4085/1062-6050-47.6.08 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3499892/